Field of the Invention
The present invention relates to a wafer processing method which can attain sufficient die strength and a sufficient gettering effect of each device obtained by dividing a wafer.
Description of the Related Art
A plurality of devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integrations) are formed on the front side of a wafer so as to be separated by a plurality of crossing division lines. The back side of the wafer thus having the devices on the front side is ground to reduce the thickness of the wafer to a predetermined thickness. Thereafter, the wafer is divided into individual device chips along the division lines by using a dicing apparatus. The device chips thus divided from the wafer are used in various electronic apparatuses or the like.
Further, a package device called MCP (Multi Chip Package) has also been put into practical use (see Japanese Patent Laid-open No. 2009-26992, for example). This package device is obtained by the steps of grinding the back sides of plural wafers to reduce the thickness of each wafer to 100 [μm] or less and next stacking these wafers to connect the terminals of upper and lower devices of the stacked wafers, thereby improving the function as a whole.
The devices included in the wafer are formed on the front side of a silicon substrate. The back side of the silicon substrate (wafer) is ground to reduce the thickness of the wafer to a predetermined thickness. Thereafter, the wafer is divided into the individual device chips. However, when the back side of the wafer is ground, grinding strain is left on the back side of the wafer to cause a reduction in die strength of each device. To cope with this problem, the back side of the wafer is polished by using a polishing pad after grinding, thereby removing the grinding strain to improve the die strength of each device (see Japanese Patent Laid-open No. 2006-80329, for example). Further, there has also been proposed a technique of forming a silicon nitride film by a plasma CVD (Chemical Vapor Deposition) method or a method of nitriding silicon, thereby forming a gettering layer for capturing heavy metal (see Japanese Patent Laid-open No. 2009-117653, for example).